In addition to "Persons", also "Relations" with reduced UI

Some customers do not plan transportation based on specific people, but rather on anonymous routes. There is always a connection between boarding→departure and a certain number of people who have to be transported on this relation.

In principle, this can be mapped with "persons" (if you name them differently), but many parts of the person UI are therefore superfluous.

We should make it possible to record relations as well as persons and adapt the UI to this way of working.